Utilization of phosphoric acid in the preparation of greases



United States Patent UTILIZATION OF PHOSPHORIC ACID IN THE PREPARATIONOF GREASES Arnold J. Morway, Clark, N.J., assignor to Esso Research andEngineering Company, a corporation of Delaware No Drawing. Filed Nov.30, 1955, Ser. No. 550,173

7 Claims. (Cl. 25240.7)

This invention relates to lubricating grease compositions, and moreparticularly to high temperature lubricating greases thickened withneutralized products of a blend of low molecular weight carboxylicacids, high molecular weight carboxylic acids and phosphoric acid. Thelubricating grease compositions of the invention have outstandingextreme pressure characteristics in addition to other desirable greasecharacteristics.

In brief, this invention relates to the utilization of phosphoric aciddirectly in combination with a low molecular weight carboxylic acidhaving from about 1 to 3 carbon atoms per molecule and a high molecularweight carboxylic acid having from about 12 to 30 carbon atoms permolecule. These blends of phosphoric acid and organic carboxylic acidsare neutralized with metal hydroxides or carbonates to provide thegrease thickening agents of this invention.

The use of small amounts of a metal salt of phosphoric acid inlubricating grease compositions has been suggested in the prior art. InUS. Patent No. 2,513,680 to Schott and Armstrong, for example, less thanabout 2.0% by weight of calcium phosphate is employed to improve theskin hardening and storage stability properties of calcium base greasesthickened with a large amount of calcium soap. The use of more thanabout 2.0% by weight of phosphoric acid is taught to be definitelydetrimental, and higher amounts to be positively destructive.

.It has now been found that excellent lubricating grease compositionscan be prepared by utilizingfrom about 2.5 to wt. percent, preferablyfrom about 2.5 to 6 wt. percent, of phosphoric acid in combination withabout 10 to wt. percent of a low molecular weight carboxylic acid suchas acetic acid and about 2 to 10 wt. percent of a high molecular weightcarboxylic acid such as stearic acid. As previously stated, thelubricating grease compositions of the invention are particularlycharacterized by high dropping points and outstanding load carryingproperties. The greases exhibit these properties regardless of whether.they are prepared in either. the hydrous or anhydrous form. j

It is notknown exactly whatfreactions the phosphoric acid enters intoduring the preparation of the greases of this invention. However, forthe present purposes it is sufiicient to note that stable lubricatinggrease compositions are prepared by the use of blends of the lowmolecular weight carboxylic acids, phosphoric acid and high molecularweight carboxylic acids, wherein the phosphoric acid contributes in somemanner to the production of effective lubricating grease compositions.The phosphoric acid may be utilized in concentrations ranging from about5 to 100%.

Suitable low molecular weight carboxylic acids are the saturated andunsaturated aliphatic carboxylic acids having from about 1 to 3 carbonatoms per molecule. Examples of such acids include formic acid, aceticacid, propionic acid, etc. Acetic acid is preferred and may be eitherglacial acetic acid or an aqueous solution thereof, the concentration ofthe acetic acid in the aqueous solution varying from about to 99.9 wt.percent. Substituted acetic acids having two carbon atoms per moleculesuch as chloro-acetic acid, glycolic acid, thioglycolic acid, glycine,etc. may also be used to modify the structure of lubricating greasecompositions made in accordance with this invention. The amount of lowmolecular weight carboxylic acid employed will be within the range ofabout 10 to 15 wt. percent, preferably about 10 to 12 wt. percent, basedon the total lubricating grease composition.

High molecular weight carboxylic acids containing from about 12 to 30,preferably about 18 to 22, carbon atoms per molecule are useful for thepurposes of the present invention. These acids may be derived fromsaturated or unsaturated naturally occurring or synthetic fattymaterial. The fatty acids normally used in the manufacture ofconventional greases, particularly the more saturated acids, arepreferred. Examples of such acids include lauric, myristic, palmitic,stearic, monoand poly-hydroxy stearic and arachidic acids as well ashydrogenated fish oil and tallow acids. Unsaturated fatty acids such asoleic, ricinoleic and similar acids may also be used. The amount of highmolecular weight fatty acids employed in preparing the lubricatingcompositions of this invention will be from about 2 to 10 wt. percent,preferably about 2 to 5 wt. percent, based on the total lubricatinggrease composition.

In general, the mol ratio of low to high molecular weightcarboxylicacids will range from about 10:1 to 30:1, preferably about 15:1 to 25:1,and the mol ratio of the average of the low molecular weight acids, i.e.the low molecular weight carboxylic acids and the phosphoric acid, tothe high molecular weight carboxylic acids will be from 20:1 to 35:1,preferably about 25:1 to 30:1.

The metals suitable for neutralizing the above blend of acids are thealkaline earth metals: calcium, barium, magnesium and strontium. Theabove metals are generally employed in the form of hydroxides orcarbonates, and the process of this invention will utilize from about 8to 15 wt. percent, based on the total lubricating grease composition, ofthe metal hydroxide or carbonate. Calcium hydroxide is preferred.Mixtures of the above metals may also be employed, if desired.

The lubricating oils employed as the mens-trua of the lubricantcompositions of this invention may be either conventional grease-makingmineral oils or synthetic lubricating oils. In general, the mineral andsynthetic lubricating oils should have a viscosity within the range ofabout 50 to 2000 S.U.S. at 100 F. and about 30 to 220 S.U.S. at 210 F.,an ASTM pour point of about +20 to F., a flash point of about 350 to 650F., and a viscosity index of about 0 to 60, although lubricating oilshaving a viscosity index of or higher can also be employed.

The synthetic lubricating oils include esters of monobasic acids (e.-g.-an ester of C 'Oxo alcohol with C Oxo acid, an ester of C Oxo alcoholwith octanoicacid, etc.), esters of dibasic acids (e.g. di-Z-ethyl hexylsebacate, di-nonyl adipate, etc.), esters of glycols (e.g. C Oxo aciddiester of tetraethylene glycol, etc.), complex esters (eg. the complexester formed by reacting one mole of tetraethylene glycol with two molesof sebacic acid and two moles of 2-ethyl-hexanol, a complex ester formedby reacting one mole of azelaic acid, one mole of tetraethylene glycol,one mole of C Oxo alcohol and one mole of C Oxo acid, etc.), esters ofphosphoric acid (cg. the ester formed by contacting'three moles of the"mono-methyl ether of ethylene glycol with one mole of phosphorousoxychloride, etc.), halocarbon'oils (e.g..the polymer ofchlorotrifiuoroethylenecontaining twelve recurring units ofchlorotrifluoroethylene),. alkyl' silicates (cg. methyl polysiloxanes,ethylpolysiloxanes, methylphenyl polysiloxanes, etc.), sulfite esters(e.g..the ester. formed by reacting one mole of sulfur oxychloride withtwo moles of the methyl ether of ethylene glycol, etc.), carbonates(e.g. the carbonate formed by. reacting C Oxo alcohol with ethylcarbonate to form a half esterand reacting this half ester withtetraethylene glycol),

mercaptals'(e.g. the mercaptal'forined by reacting Z-ethyl hexylmercaptan with formaldehyde), formals (e.g. .the

formal formed by reacting C Oxo alcohol with'formaldehyde), polyglycoltype synthetic oils (e.g. thecompounds formed by condensing butylalcohol, with fourteen units of propylene oxide, etc.), or mixtures ofthe above in any proportions.

The lubricating grease compositions of the invention will contain fromabout 50 to 90 wt. percent, preferably about 65 to 85 wt. percent, ofthe mineral and/or synthetic lubricating oil and about 10 to 50 wt.percent, pref-- erably about 15 to wt. percent, of the reaction prodnetsof blends or mixtures of the above acids with the metal base.

Conventional lubricating grease additives may alsobe employed in thelubricating grease compositions of the 1 present invention. Suchadditives, for example, include: oxidation inhibitors such as phenylalpha naphthylamine, corrosion inhibitors such as sorbitan monooleate,tackiness agents such as polyisobutene or high molecular weightpolymerized acrylic esters, and the like.

In general, the lubricating grease compositions of this invention may beprepared by coneutralizing the blend or mixture of phosphoric acid, thelow molecular weight carboxylic acids and the high molecular weightcarboxylic acids with the metal base, e.g. hydrated lime, and dispersingthe products in the lubricatingoil. It is not essential that the waterof reaction be removed. However, a somewhat greater stability can beachieved when the water of reaction is removed by carrying out thegrease preparation at elevated temperatures.

The preferred method of preparing the-lubricating grease compositions ofthis invention involves mixing the metal base and the lubricating oiltogether at. room temperature to form an intimate slurry. The highmolecular weight carboxylic acid is added to the slurry with stirring. Ablend of the low molecular weight carboxylic acid and the phosphoricacid'is then added with continued mixing, and a solid grease formsalmost instantaneously with the temperature rising to about. 180 to 210reciprocal seconds.

If desired, the lubricating grease compositions of this 1 invention'mayalso be prepared by heating the grease batch to a temperature of about400 to 550 following of shear within the range of about 100,000 to500,000"

the addition of the blend of low molecular weight car-' boxylic acid andphosphoric acid.. The heated grease batch is then cooled to atemperature of about to F. with stirring and the conventional greaseadditives charged. This lubricating grease composition may also befinished by homogenization.

The invention will be more fully understood by reference to thefollowing specific examples illustrating various modifications of theinvention.

EXAMPLE I A lubricating grease composition according to this inventionwas prepared from the following constituents:

Formulation Percent Weight Glacial'acetic acid 12. Ste ric acid I 3.Phosphoric acid (85% cone.) 3. Hydrated li a 10. Phenyl alphanaphthylaminej'n' 0. Mineral libricating oil, 55 SUS @,210v F 70. M01ratio of acetic acid'to stearic-acid 20: M01 ratio of low mol. wt. acids(i.e

phoric acid) to stcaric acid 22. 8:

Preparation The hydratedlime andthe mineral lubricating oil were mixedtogether at room temperature (about 70 F.) .to

form an intimate slurry. The stearic acid as a powder.

was added to the lime slurry A blend of the acetic and phosphoric acid.was thenadded, A solid grease formed.

immediately with the temperature rising to about F.-

The phenyl alpha naphthylamine was added, and the stirring continued forabout two-hours untilthe temperature subsided. The grease washomogenized by being passed through a Morehouse mill.

The above data show that the lubricating grease.1com-..

positions encompassed by this invention have very'desirable high"temperature stability and extreme pressure characteristics.

EXAMPLE 1t Formulation Percent Weight Glacial acetic acid 12. 0 Stearicacid 3.0 Phosphoric acid (85% cone.) 3.0 Hvdratcd lim 11. 6 Phony] alphanaphthylaminm; 0.5 Mineral l'lbricating oil, 55 SUS 210 F 69.9 Mol ratioof accti: acid to stcaric acid..- 20:1 Mol ratio of low mol. wt. acids(in. acetic acid plus phosphoric acid) to stearic acid 22:8:1

Preparation Similar to that" described in Example I, except thatfollowing the'addition of the blend of acetic acid and phosphoric acidthe grease mixture was heated ito a temperature'of about 500 F. Theresulting 1greasejcomposition then cooled to, about200"F."withstirring,and

H HQUNEOOCO the phenyl alpha naphthylamine added. The grease was thenGaulin homogenized at 6500 p.s.i.

Properties Appearance Excellent, uniform product. Dropping point, F.500+. Penetration, 77 F. mm./10':

Unworked 210. Worked 60 strokes 230. Worked 230,000 strokes 300 (118F.). Cooled to 77 F. reworked 60 strokes 330. Phase change up to 450 F.None. E. P. properties, Timken test (50 lbs.

load) Pass, narrow scar. Norma Hoffman oxidation test (hrs.

to 5 psi. drop) 420. Lubrication life, hrs. (250 F.-

10,000 r.p.m.) 1200+.

1 N failure-test discontinued.

The grease of Example II also showed the desired high temperature,stability and load carrying properties of the grease prepared inaccordance with the method described in Example I, though the former wasprepared at a much higher temperature to effect dehydration.

It will be further understood that the present invention is notnecessarily limited to the specific materials and conditions of theforegoing examples. These materials and conditions may be varied withinthe limits indicated in the general portions of the specification.

What is claimed is:

1. A lubricating grease composition comprising a major proportion oflubricating oil thickened with a grease thickening amount of an alkalineearth metal base neutralized mixture of high molecular weightmonocarboxylic acids having about 12-30 carbon atoms per molecule, lowmolecular weight monocarboxylic acids having from about 1-3 carbon atomsper molecule, and phosphoric acid, the amount of said phosphoric acidbeing 2.5 to 10.0 wt. percent, wherein the mole ratio of low molecularweight acids to high molecular weight carboxylic acid is about 20:1 to35:1 and wherein the mole ratio of said low molecular weight carboxylicacid to said high molecular weight carboxylic acid is about 10:1 to30:1.

2. The composition of claim 1 wherein said alkaline earth metal base isa calcium base.

3. The composition of claim 1 wherein said lubricating oil is a minerallubricating oil.

4. A lubricating grease composition comprising a major amount of minerallubricating oil and about 10 to wt. percent of the alkaline earth metalsalts of a C to C fatty acid, a C to C fatty acid and phosphoric acid,the amount of phosphoric acid being about 2.5 to 10.0 wt. percent,wherein the mole ratio of low molecular weight acids to high molecularweight carboxylic acid is about 20:1 to 35:1, and wherein the mole ratioof acetic acid to said C to C fatty acid is about 10:1 to 30:1.

5. A grease composition according to claim 4, wherein said alkalineearth metal is calcium and said C to C fatty acid is acetic acid.

6. The method of preparing a lubricating grease composition whichcomprises dispersing a metal base in a lubricating oil, adding to theresulting dispersion high molecular weight carboxylic acids having fromabout 12 to 30 carbon atoms per molecule, then adding a blend of lowmolecular weight carboxylic acids having about 1 to 3 carbon atoms permolecule and phosphoric acid wherein the mole ratio of low molecularweight carboxylic acid to high molecular weight carboxylic acid is about10:1 to 30:1 and wherein the mole ratio of said low molecular weightcarboxylic acid and said phosphoric acid to said high molecular weightcarboxylic acid is about 20:1 to 35:1 and thereafter cooling theresulting grease mixture to obtain said lubricating grease composition,said metal base being present in suflicient amounts to neutralize saidacids and the amount of said phosphoric acid being 2.5' to 10.0 wt.percent.

7. The method of claim 6 wherein said grease mixture is heated to atemperature of about 400 to 550 F. subsequent to the addition of theblend of low molecular weight carboxylic acid and phosphoric acid.

References Cited in the file of this patent UNITED STATES PATENTS2,417,430 McLennan Mar. 18, 1947 2,417,431 McLennan Mar. 18, 19472,417,433 McLennan Mar. 18, 1947 2,513,680 Schott et a1. July 4, 19502,846,392 Morway et al. Aug. 5, 1958

1. A LUBRICATING GREASE COMPOSITION COMPRISING A MAJOR PROPORTION OFLUBRICTING OIL THICKENED WITH A GREASE THICKNENING AMOUNT OF AN ALKALINEEARTH METAL BASE NEUTRALIZED MIXTURE OF HIGH MOLECULAR WEIGHTMONOCARBOXYLIC ACIDS HAVING ABOUT 12-30 CARBON ATOMS PER MOLECULE, LOWMOLECULAR WEIHT MONOCARBOXYLIC ACIDS HAVING FROM ABOUT 1-3 CARBON TOMSPER MOLECULE, AND PHOSPHORIC ACID, THE AMOUNT OF SAID PHOSPHORIC ACIDBEING 2.5 TO 10.0 WT. PERCENT, WHEREIN THE MOLE RATIO OF LOW MOLECULARWEIGHT ACIDS TO HIGH MOLECULAR WEIGHT CARBOXYLIC ACID IS ABOUT 20:1 TO35:1 AND WHEREIN THE MOLE RATIO OF SAID LOW MOLECULAR WEIGHT CRBOXYLICACID TO SAID HIGH MOLECULR WEIGHT CARBOXYLIC ACID TO 10:1 TO 30:1.